Moreover, to date, various kinds of chelating agents, ion exchange materials, alkalizing agents, and dispersants have been known to be used for builders to be blended in detergents. Particularly, the phosphoric acid-based chelating agents such as tripolyphosphates as a main component thereof have good water solubility and detergency, so that they have been formulated as main detergent builder components.
In recent years, however, the use of tripolyphosphates has been decreased, since they can cause eutrophication in closed water areas such as lakes and marshes. Instead, crystalline aluminosilicates (zeolites) have been commonly used as substitutes for the metal ion capturing agent, as typically disclosed in Japanese Patent Laid-Open No. 50-12381, of which the disclosure is incorporated herein by reference. Such detergents formulating zeolites as mentioned above would require a standard amount of dosage of 40 g per one washing cycle, the washing cycle being most commonly using about 30 L of the washing liquid per one cycle in Japan. Also, the powder detergents available at that time had a low bulk density at a level of 0.20 to 0.45 g/ml owing to the solubility in cold water. As a result, the standard volumetric amount is made as high as about 90 to about 200 ml of detergents per 30 L of water for washing, so that much inconveniences were caused in handling during distribution, and in shops and households.
Therefore, an intense investigation has been made to produce compact detergents. For instance, Japanese Patent Laid-Open Nos. 62-167396, 62-167399, and 62-253699, of which the disclosure is incorporated herein by reference, disclose a remarkable decrease in the amount of crystalline inorganic salts such as sodium sulfate used as powdering aids conventionally contained in detergents. In addition, Japanese Patent Laid-Open Nos. 61-69897, 61-69899, 61-69900, and 5-209200, of which the disclosure is incorporated herein by reference, disclose that an increase in the bulk density of the detergents. By these findings, detergents having a bulk density of from 0.60 to 1.00 g/ml, whose standard amount of dosage is from 25 to 30 g/30 L, can be produced, thereby resulting in making the detergents compact to a level of a standard volumetric amount of from 25 to 50 ml/30 L.
However, in conventional detergents, a large amount of surfactants had to be blended in the detergent compositions because mainstream of the technical idea was to make the oily components in dirt soluble by surfactants. Specifically, sebum dirt stains ascribed to human bodies, the most typical dirt stains adhered to clothes (most likely to be observed on collars and sleeves), are taken as examples. The sebum dirt stains contain oily components, such as free fatty acids and glycerides, with a high content of 70% or more (Ichiro KASHIWA et al., "Yukagaku," 19, 1095 (1969), of which the content is incorporated herein by reference). The oily components lock carbon and dirt in dust and peeled keratin, so that the resulting substance is observed as dirt stain composites. In order to wash off the sebum dirt stains, conventionally detergents are designed based on a washing mechanism mainly by making these oily components soluble with micelle of surfactants, thereby detaching carbon, dirt, and keratin from clothes. This technical idea has been widely established among those of ordinary skill in the art, and even when the conventional detergents are shifted to compact detergents, substantially no changes took place in the surfactant concentration in the washing liquid. This fact is described in "Dictionary for Detergents and Washing," Haruhiko OKUYAMA et al., p. 428, 1990, First Edition, Asakura Publishing Company Limited, of which the content is incorporated herein by reference. It can be inferred that there are substantially no changes in concentrations in the washing liquid for components other than sodium sulfate.
Based on these washing principles, the surfactant concentration in the washing liquid has to be made high in order to achieve high washing power, so that a large amount of surfactants has to be blended in the detergent composition. In other words, in a case where the standard amount of dosage is simply reduced in the conventional detergent compositions, the absolute amount of the surfactants in the washing liquid is evidently reduced. Therefore, in a system where the detergency is dependent upon the micelle-formation ability of the surfactants, which is based on a conventional technical idea, a relative surfactant concentration in the compositions has to be increased even when the standard amount of dosage is reduced, so that the balance in the detergent composition between the surfactant to be needed and other components is lost. Therefore, a further reduction in the standard volumetric amount was deemed to be technically extremely difficult problem.
On the other hand, crystalline alkali metal silicates having particular structure disclosed in Japanese Patent Laid-Open Nos. 5-184946 and 60-227895, of which the disclosure is incorporated herein by reference, shows not only good ion exchange capacity but also actions of alkalizing agents (alkalizing ability). Therefore, possibility of more compact detergents has been studied because both of the functions which conventionally have been satisfied by two different components, including metal ion capturing agents, such as zeolites, and alkalizing agents, such as sodium carbonate, can be satisfied with the above crystalline alkali metal silicates alone.
For instance, Japanese Patent Laid-Open No. 6-116588, of which the disclosure is incorporated herein by reference, is concerned with a detergent composition containing a crystalline alkali metal silicate. In Examples of this publication disclosing a more compact detergent, even in a case where the amount of the detergent composition at washing is reduced by 25% by weight, the detergent composition has a washing power substantially the same as conventional detergent compositions. However, the composition is formulated based on the conventional washing principle, and the composition is obtained by simple replacement of the alkalizing agent and the ion exchange material with the crystalline alkali metal silicate. Therefore, the ion exchange capacity are ascribed solely to the crystalline alkali metal silicates contained therein, so that the ion exchange capacity is deficient for that needed for detergent compositions. In this case, the functions of the crystalline alkali metal silicates as alkalizing agents are prioritized over their functions as metal ion capturing agents, so that the washing power of the detergent composition is not always satisfactory, owing to the fact that the washing power of the detergent composition is likely to be affected by the water hardness of water for washing. Therefore, if the amount of dosage of the detergent composition were reduced, a good washing power is not able to be maintained.
A number of patent applications have been filed concerning the crystalline silicates disclosed in Japanese Patent Laid-Open No. 60-227895, of which the disclosure is incorporated herein by reference. Japanese Patent Unexamined Publication No. 6-502199, of which the disclosure is incorporated herein by reference, discloses a detergent comprising a layered crystalline silicate, a zeolite, and a polycarboxylate in particular proportions, to thereby provide a detergent which is free from providing film layer formation on fibers and has excellent washing power and bleaching agent stability. However, under the blending conditions given in this publication, when the amount of the detergents added was reduced at washing, the alkalizing ability is deficient because the amount of the crystalline alkali metal silicate in the builder composition is small, thereby making it impossible to maintain good washing power. Also, this publication never teaches the technical idea that an excellent washing power is exhibited in a small amount of dosage of detergents.
The same can be said for detergents containing crystalline alkali metal silicates disclosed in Japanese Patent Unexamined Publication 6-500141, Japanese Patent Laid-Open Nos 2-178398 and 2-178399, each of which the disclosure is incorporated herein by reference. None of the references do not pertain to detergents used in a small amount of dosage as taught in the present invention. Rather, in the case where the amounts of the detergent compositions shown in each of Examples are reduced, the washing power is lowered.
Japanese Patent Laid-Open No. 7-53992, of which the disclosure is incorporated herein by reference, discloses that the amount of dosage per cycle is reduced by formulating the layered crystalline silicate disclosed in Japanese Patent Laid-Open No. 60-227895, together with other builder components such as alkalizing agents and metal ion capturing agents, wherein the layered crystalline silicate is added in excess to the builder components. The technical idea disclosed herein is a conventional idea simply rephrasing that the alkalizing agents and the metal ion capturing agents added as two components are substituted with a single component of the crystalline alkali metal silicate, and thereby the resulting compositions have detergency notably impaired by the changes in the water hardness of tap water. Therefore, it would be difficult to attain sufficient detergency with a standard amount of dosage of 20 g or less per 30 L of water for washing under the water hardness conditions in Japan. And as the water hardness increases, the detergency is likely to become lower than that of conventional detergents.
Accordingly, an object of the present invention is to provide a detergent composition for clothes washing exhibiting excellent detergency even at a low surfactant concentration.
Another object of the present invention is to provide a process for washing clothes using the above detergent composition.
These and other objects of the present invention will be apparent from the following description.